1. Field of the Invention
The invention relates to a method and device for measurement of inclination relative to a horizontal plane. The invention in particular relates to such a device having a display which shows unambiguously how the device should be rotated to achieve level or plumb.
2. Description of the Prior Art
Various inclination measuring devices including carpenters' levels (also called torpedo levels) are well known in the art and indicate level and/or plumb by use of a bubble in a sealed tube of liquid. Also well known are electronic levels which provide an indication in addition to level and plumb such as a digital readout. These electronic levels typically provide a system of lights or other indications of the level, plumb, or non-level or non-plumb conditions.
U.S. Pat. No. 4,912,662 issued Mar. 27, 1990 to Butler et al discloses an inclinometer which provides various methods of showing the level or plumb or other inclination condition of the device. With reference to FIG. 1 herein, which is also FIG. 1 of the above referenced patent, an inclinometer 20 includes one of a number of different length rails such as 22, in which is removably inserted an electronic measurement unit 24 which has an outer housing 26. The face of the electronic measuring unit 24 includes a mode selector 28, a recalibration selector 29, and an accuracy range selector 30. The face of unit 24 includes a combination degree, percentage and rise/run indicator 32, three seven element alphanumeric indicators 34, a low battery indicator 36, and direction indicator 38 which indicates which direction inclinometer 20 should be moved in order to obtain a level or plumb reading. The mode selector 28 allows a selection of display modes which can selectively provide digital displays such as the angle, the rise/run, the percent slope, and also an analog display.
The analog display as shown in FIGS. 2A, 2B, and 2C (also from U.S. Pat. No. 4,912,662) includes a level indicator as shown in FIG. 2A which comprises two dots. In FIG. 2B, the indicator includes three vertical lines located to the right of the dot, indicating the right side of the unit 24 is high. FIG. 2C indicates that the left side is high. The degree that either side is high is indicated by the number of lines to the right or left of the two dots. Thus, three lines to the right of the two dots indicates that a level is higher to the right side than the .level would be if only one line were displayed.
In the system of Butler et al. the arrows 38 indicating in which direction the inclinometer should be moved are inherently ambiguous because they are arranged vertically, while clearly in order to achieve a level or plumb condition the device must be rotated either clockwise or counter-clockwise.
Furthermore, the analog displays shown in FIGS. 2A, 2B, and 2C while they show which side is high, this is not inherently obvious from the display but must be learned from the instructions provided or from repeated use of the device. Furthermore, the mere indication of which side of the level is high or low does not unambiguously indicate how the device should be rotated to achieve the level condition as shown in FIG. 2A.
This device while providing much useful information is rather complex to use, requiring a significant amount of understanding and/or training on the part of the user.
It would be extremely useful to have a level which has a display which unambiguously shows how the device (and the associated work piece such as a board) is to be rotated to achieve the level/plumb condition. This is especially true with such electronic levels which do not have the inherently understandable display of the basic bubble in a tube, and instead rely on some electric or electronic indication such as lights or numbers.